Compressor unloader



April 1962 H. R. JAQUITH ETAL 3,030,928

COMPRESSOR UNLOADER Filed Aug. 29, 1958 v 29 WII INVENTOR. Howard R. Juquifh y Harvey A. Klumb 3,030,928 COMPRESSOR UNLOADER Howard R. Jaquith, Rochester, and Harvey A. Klumb,

Pittsford, N.Y., assignors to Taylor Instrument Companies, Rochester, N.Y., a corporation of New York Filed Aug. 29, 1958, Ser. No. 758,142 7 Claims. (Cl. 121-38) This invention relates to compressor unloaders, in particular to quick-aoting relays or operators for actuating or operating the unloading device or devices of an aircompressor.

In the prior co-pending application of A. W. Griswold et al., S.N. 612,460, filed September 27, 1956, now Patent No. 2,979,068, and entitled Compressor Unloader, there is disclosed and claimed a regenerative compressor unloader operator and compressor unloading system. The goal of the present invention is to provide corresponding entities of less elaborate and more economical nature. The invention of Griswold et a1. is so conceived as to require an unloader operator of a type capable of coacting with similar operators in a relatively complex manner so as to provide a given sequence of unloading steps.

However, many compressor control situations are satisfied by a less complex control system, such as might be provided for operating one or two or more unloading devices sequentially and cumulatively as, for example, in a two-device, three-step scheme wherein both unloading devices are operative to unload, then just one, and subsequently, neither, corresponding respectively to minimum, intermediate and maximum capacity operation of a compressor thus controlled.

In unloading schemes of this simple type, it is practical to provide an unloading device operator that operates completely functionally independently of any additional operator, and in which the design factors of ruggedness, simplicity and compactness can be favored because of such functional independence.

Hence, one object of our invention is to provide a novel relay or operator construction that is compact, rugged and completely independent, operatively speaking, of any additional relay or relays that might be used in an unloading system therewith.

Upon starting up a compressor, that is, causing a motor or the like to rotate fan blades, to begin moving pistons, or initiate other operations involved in the characteristic function of a given compressor, it is desirable to get said compressor into substantially full swing insofar as is concerned the mechanical motion involved in com pression is concerned, but without compression occurring, i.e., without loading the compressor.

In line with this consideration, another object of the invention is to provide a novel compressor control system wherein the compressor is automatically subjected to minimum load when started up as aforesaid, but wherein, once the mechanical aspect of compressor operation is in full swing, the said compressor is automatically caused to compress in the usual manner, for the purpose of supplying compressed gas to a compressed-gas receiver or reservoir.

Finally, compressor unloader operation is only one of many applications of a quick-acting, substantially on-oif, or snap-acting relay or operator. Those skilled in the art will be aware of many such applications, e.g., quick and positive openings and closings of such devices as valves, electrical switches, etc., in general.

Therefore, a further object of our invention is to provide a novel quick-acting relay which converts an input or signal, such as fluid pressure, into a motion against an opposing biasing force, and, when a certain extent of motion occurs, decreases said biasing force, whereby tatcs Patent further motion is obtained independently of the said input or signal.

The significance of such regenerative motion is that it provides a mode of closely approximating instantaneous application of valve or switch-operating force at full strength to the valve, switch or analogous device which it is desired to operate. If the force for operating a compressor clearance pocket is allowed to build-up its effect proportionally on said pocket, the Valve constituting the essential element of such pocket may chatter or pound on its seat during the portion of build-up time wherein the operating force is not much more than enough to just begin moving the valve away from its seat, unless such build-up time is quite short. Such phenomena as chatter or pounding contribute much to the wear and tear involved in use of the clearance pocket, or analogous device.

Further objects of our invention will become apparent as the disclosure proceeds.

In the drawings, FIGURE 1 represents a regenerative compressor unloader operator or relay, shown in section, in a compressor system, shown diagrammatically.

FIGURE 2 is a detail of a bleed device adapted to be utilized in FIGURE 1.

FIGURE 3 shows a means for adjusting the dead band of a relay such as shown in FIGURE 1.

FIGURE 4 is an isometric view of a dual operator, consisting essentially of two relays such as shown in FIGURE 1.

A relay or operator 0 according to the invention may be visualized as embodied in the familiar stacked-type construction, shown in a diametric section (in FIGURE 1) of an assembly of more or less cylindrical, coaxial elements including body parts 1, 2, 3 and 4, diaphragms 13 and 14, and other entities to be described, that are arranged along a vertical axis in the plane of the drawing and through-which axis the said section is taken.

Body parts 1, 2 and 3 are secured directly together by any convenient means (not shown) and body part 4 is secured to body part 3 by posts 25. Thus, the said body parts define an essentially cylindrical assembly incorporating the elements of the relay.

Body part 1 includes the unloading device operator proper, i.e., a ball 5 on a rigid stem 6, coacting as a valve with a pair of annular seats 7 and 8. Seat 7 is the inner end of a cylindrical axial bore 9 in body part 1. Seat 8, however, is the inner periphery of a circular aperture in the bottom of a cup 10 secured by any convenient means (not shown) in an axial cylindrical bore in body part 1. The last said bore is joined to bore 9 by a chamber 11 which receives ball 5. Bore 9 communicates with the atmosphere exterior to body part 1, while a port 12, provided for the purpose of connecting an unloading device to the operator 0, communicates with chamber 11.

For the purpose of operating the ball 5, a pair of slack diaphragms 13 and 14 are provided, the central portions of which are secured together and to stem 6 by any convenient means, such as pairs 15 and 16 of clamping plates or members. The peripheries of diaphragms 13 and 14 are clamped between body parts 1, 2 and 3 so as to define chambers 17, .18 and 19 in body parts 1, 2 and 3 respectively, said body parts being provided with board portions of diameter corresponding to the movable portions of diaphragms 13 and '14, and of sufficient depth to allow said diaphragms to move the ball 5 into sealing engagement with either of seats 7 and 8.

Stem 6, or a rigid extension thereof, extends into an axial cylindrical bore 20 in body part 3, and in order to seal chamber 19 off from connnunication to the atmos phere via bore 20, a seal 21 is provided in bore 20 for stem 6. Said seal may be an O-ring compressed between the bore wall and the periphery of the stem so as to permit the stem to move in said bore While sealing the annular interstice between the bore and the stem.

Chamber 18 is vented to atmosphere via a port 22. Chamber 17, and the interior of cup 10 are connected to a port 23, which port is adapted to be connected to a source of pressure fluid for actuating an unloading device connected to port 12, an aperture 24 in the wall of cup 10 permitting passage of fluid from port 23 to the chamber 17 via the interior of cup 16.

Chamber 19 also communicates with the interior of cup 10, via aperture 26 in the wall of cup 10, an L-shaped passage 27 having a restriction 28 therein in body part 1, a passage 29 in body part 2, and a passage 30 in body part 3, passage 36 opening into bore 20 below seal 21.

Diaphragm 14 is of sufficiently greater area than diaphragm 13 that if the same value of pressure acts downwardly on diaphragm 14 as acts upwardly on diaphragm 13, the net force on stem 6 will be downwardly directed. On the other hand, if the pressure on diaphragm 14 is enough less than the pressure on diaphragm 13, the net force on stem 6 will be directed upwardly.

Obviously, then, if the pressure on diaphrgam 14 is controlled by bleeding it to atmosphere at an arbitrarily variable rate, say ranging from a bleed rate at which air escapes from chamber 19 faster than it can be supplied thereto viaorifice '28, to a zero or minimum bleed rate such that the pressure in chamber 19 can build up to a value sufliciently high that the diaphragm area-ditferential can cause the net force on stem 6 to be downwardly directed.

As shown, a bleed device is provided in the form of a nozzle 31 having a ball 32 seated in the upper end of said nozzle and arranged to close the nozzle opening unless blown 011 by fluid escaping through said nozzle. Accordingly, if for the time being nozzle 31 be imagined to be freely connected to passage 27 downstream of restriction 28, and a source of pressure fluid such as compressed air is connected to port 23, the pressure in chamber 19 will be a function of the extent to which ball 32 can be made to obstruct flow from nozzle 31. Nozzle 31 as shown is exteriorly threaded and screwed into a tapped portion 33 of bore 34.

Body part 4 has a passage 36 connecting at one end with a source of some external pressure, such as a compressed air receiver R, and connecting at its other end to a bellows 38 mounted on the underside of body part 4. A cup 39 receives the free portion of bellows 38 and is maintained in position by a compression spring 40 compressed between a flange 41 on the tlip of cup 39 and an abutment comprising an interiorly threaded ring or collar 42 and an exteriorly threaded projection 43 of body part 3, said flange being threaded on said projection. The parts just described are shown with the bottom of cup 39 far short of causing ball 32 to throttle the opening of nozzle 31, bellows 38 having been extended a fraction of inch or so by increasing receiver pressure before coming into contact with ball 32.

However, it is obvious from what has been said so far, that should the receiver pressure increase enough to force ball 32 to seat on the nozzle opening, pressure in chamber 19 would increase until ball was driven to seat 7, thus ermitting supply pressure from port 23 to be admitted to a valve V, an air-to-open valve having a pressure responsive diaphragm motor biased to maintain the valve closed in the absence of suflicient pressure acting on the motor. As thus far described, this is a known mode of quick operation of a valve, bleed devices of the class including the baflle and nozzle type being quite sensitive to relativey minute changes in spacing between battle and nozzle, once the said spacing decreases to where the baffie begins to throttle flow from the nozzle. The bleed device is in effect a valve needing only a very slight and low-powered actuating motion for fully closing or fully opening the valve. Such sensitivity is gained at the expense of slowing down build-up of pressure upstream of the bleed device upon closure. That is, the usual supply fluid metering orifice 28 is provided.

Moreover, even though ball 32 may have to move but one or two thousandths of an inch in order to encompass both its minimum and maximum throttling elfect of the nozzle, it is possible for receiver pressure to move the ball to intermediate batliing positions, rather than through the whole range of movement. In such case, ball 5 would be left between seats, wasting air to atmosphere but not fully applying or fully releasing supply pressure respectively to or from the motor of valve V. Therefore, the plug, gate or the like of the valve V may be held closed or open with insufiicient force to maintain the valve in such position in the face of the peaks of pressure as would occur in a piston-type compressor on each cycle of compression. Under such conditions, compressor pressure peak would lift the plug of valve V from its seat and let it drop back thereon at the frequency of the compression cycle. Such pounding or chattering occurs with considerable force and causes undesired wear of the valve.

However, it is possible to assure the full movement of ball 5 by causing the pressure in chamber 19 to build up regeneratively after a certain point in the bathing of the nozzle 31. According to our invention, regeneration is obtained by making opposition to bellows expansion decrease at such point. In effect, this amounts to decreasing the effective spring force resisting extension of bellows 38, such force being mainly that of spring 40. Bellows 38, of course, has itself a spring constant, usually somewhat smaller than that of spring 40. According to our invention, the desired effect is obtained by providing a feedback spring 44 held in compression between the upper end of stem 6 and the bottom of cup 39. With this arrangement, receiver pressure is converted into motion of cup 39 against an effective spring force or bias arising in the material of bellows 38 and springs 40 and 44 collectively.

If it is imagined that ball 5 is seated on seat 8 and ball 32 is permitting air to escape from nozzle 31 fast enough to maintain the pressure in chamber 19 at a sufficiently low value so that the net effect of pressure on stem 6 is upward, and that receiver pressure begins to increase, eventually some point will be reached wherein springs 40 and 44 are compressed to such extent that ball 32 is held by cup 39 close enough to the opening of nozzle 31 that the pressure in chamber 19 begins to increase. Moreover, as the pressure in chamber 19 increases, there will eventually result a pressure in chamber 19 sufliciently high that the force due to the larger effective area of diaphragm 14 will predominate over the force due to the lesser effective area of diaphragm 13 and move stem 6 downward. However, as soon as downward movement of stem 6 occurs, the length of spring 44 will increase, which means that the force opposing downward motion of cup 39 will decrease. In other words, the force opposing extension of bellows 38 will decrease and permit the bellows to extend a little more without any further increase in pressure therein.

At this point, regeneration will be occurring since as long as slacking of spring 44 continues and results in downward movement of cup 39 in addition to downward movement thereof caused by increase, if any, of receiver pressure, pressure in chamber 19 will increase and cause additional slacking of spring 44.

In practice, the phenomenon of regeneration occurs substantialiy instantaneously, since as those skilled in the art will understand, a range of a thousandth of an inch or so covers the movement of ball 32 between minimum and maximum nozzle-battling effect.

As a result, valve V is caused to open quickly and positively without pounding or chattering on its seat, and, if the receiver pressure then drops otf suflicicntly, ball 5 will be quickly and positively moved upward to allow valve V to vent. The overall effect is that changes in pressure in chamber 19, are initiated by changes in receiver pressure. However, when pressure changes in chamber 19 result in beginning of movement by stem 6, the regenerative action sustains such movement.

The total vertical displacement of ball 5 is larger than the vertical displacement of cup 39 needed to traverse the full bafliing range of nozzle 31. Hence, when the compressor is loaded, the receiver pressure required to unload'is greater than the receiver pressure required to load the compressor. That is, if it takes 100 p.s.i. to get the cup to the point where it initiates unloading, and feedback spring 44 is thereby relaxed in compressive force by an amount equal to 3 p.s.i., any pressure down to 97 p.s.i. will suflice to hold ball 32 in maximum throttling position. The unloader operator may thus be said to have a dead spot or dead band of 3 p.s.i., and this dead spot is directly proportional to the spring constant of spring 44 and to the distance ball 5 travels in going from one of seats 7 and 8 to the other, but inversely proportional to the effective area of bellows 38.

While upon first glance it may seem, and it can be the case inpractice, that a dead spot in a control device is hardly advantageous, in the case of compressor unloading it is definitely an advantage, as will be evident from the considerations infra.

Where valved devices, such as clearance pockets, are utilized in on-oif fashion to control compressor loading, frequent operation of such devices occurs. Thus, valve V may be actuated between open and closed positions many times an hour, with the result of much wear on the seat and plug elements of the valve V. Such wear would be maximum if loading and unloading of a given unloading device were set to occur, and did occur, at the same pressure, and the utilization of compressed air from the compressor-receiver caused receiver pressure to fluctuate around said pressure. Naturally, the moving parts of the unloader operator will suffer like wear.

However, where a dead spot exists such as described above, receiver pressure must fluctuate the width of the dead spot before the unloader operator will act to load or unload following an unloading action or a loading action, respectively. .Thus, in the dead spot example described supra, it would be assumed that 97 p.s.i. would be a satisfactory receiver pressure insofar as was concerned utilization of the compressed air by some load, and again, itwould be assumed that it would be acceptable to allow the compressor to load as high as 100 p.s.i. before unloading. Obviously, the dead spot would be chosen so as to compromise frequency of operator action with spread between the value of unloading pressure and the value of loading pressure.

The rudimentary details of a compressor system have been sketched in FIGURE 1'. A compressor C, driven by a motor M forces air through a check valve X into a receiver R, said valve permitting compressed air to How into receiver R, while preventing backfiow from the receiver-to the compressor. The air in receiver R is applied in varying amounts to some'utilization device or load L. Receiver pressure is also admitted to bellows 38 of the unloader operator, and the valve V- accordingly is opened or closed depending on the magnitude of the receiver pressure. When valve V is open, a capacity P, i.e., a clearance pocket, is added to the compression side ofthe compressor and, hence, the output pressure of the compressor is less than it would be were valve V closed to cut-off the capacity P from the comressor. p The foregoing will be recognized as a simple prior art compressor system and need not be described further, except to say that should utilization of air by load L decrease enough, the consequent increase in receiver pressure will cause the "operator to open valve V, whereby the compression'will become too low to force check valve X open. Hence, no further increase of receiver pressure will occur. If, then, receiver pressure drops far enough, say due to increased utilization of air by load L, the operator will close valve V, and compressor C will increase its output pressure, and will remain loaded until or unless receiver pressure again reaches the point where unloading is called for.

As in any fluid-operated system or device, the various chambers and passages of operator 0, its connection to valve V, and so on, provide flow-resistance and airvolumes through, from and/ or to which fluid must flow in operation of the system. While the resistive effect of orifice 28 is deliberately introduced for the usual reasons, i.e., to minimize air consumption, to accentuate the nozzle back-pressure change consequent upon throttling or unthrottling nozzle 31, etc., it is otherwise desirable that transfer of fluid, as between the motor of valve V and atmosphere, between said valve and the pressure source connected to port 22, and so on, take place as quickly as possible. Hence, passages and connections involved in such transfer should be relatively short, direct and generous in cross-section, having in mind, however, the relative capacities of the atmosphere, or other region to which operator 0 vents, and of the supply pressure source for respectively quickly accommodating and furnishing the quantities of air being transferred.

By reason of its large capacity for air, the atmosphere is a convenient place to which to vent operator 0. Likewise, a high-capacity pressure source will assure quick pressurization of valve V when ball 5 is snapped down to seat 7.

It is also to be noted that the relative effective areas of diaphragms 13 and 14 do not alone determine the force on the stem due to the pressures in chambers 17, 18 and 19. For example, when ball 5 is on either of seats 7 and 8, it has a circular area on which pressure exerts a downward force (an area equal to the plane area circumscribed by the line of contact between ball and seat, less the cross-sectional area of stem 6), whereas an up- Ward force is exerted by the effective area of seal 21. While these additional effective areas must be taken into account when designing the operator, mechanical friction and inertia in the moving parts of the operator may be neglected without apprecaible consequences.

It should be understood that although proportions of operator 0 have been somewhat exaggerated in FIGURE 1 for clarity of illustration, relative proportions of pressure-responsive areas as illustrated correspond generally to acutal embodiments of the operator 0. However, in an actual case, full travel of ball 5 from seat to seat might be as little as five one-hundredths of an inch.

Naturally, the diameter of seats 7 and 8 would be sufficiently large that the five one-hundredths of an inch travel of ball 5 away from either seat provides an effectively unimpeded passage for air flowing past said seat.

The area proportions were conceived with the thought that the air supplied diaphragms 13 and 14 would be from a common supply or source. However, obviously separate sources could be utilized, i.e., port 22 would be connected to a pressure source capable of furnishing air at high enough pressure and in sufficient volume to open valve V quickly, whereas orifice 28 would be connected to a second pressure source that could be somewhat different in magnitude and capacity than the first said source. Where different pressure sources are utilized, the relative areas of diaphragms 13 and 14 would depend on the comparative magnitudes of pressures available from said sources. Obviously, the necessity for a difference in effective areas of diaphragms 13 and 14 depends on the fact that a common pressure source is utilized (or separate but similar sources). With separate sources, an even larger area-preponderance of diaphragm 14 over diaphragm 13 might be necessary were the pressure available for diaphragm 14 sufficiently less in magnitude than that supplied to diaphragm 13. Again, were the supply pressure magnitude-difference in the opposite sense, diaphragm 14 might be larger than, equal to or less than diaphragm 13, depending on how much larger the pressure 7 available for diaphragm 14 was than the pressure available for diaphragm 13.

In other words, the regenerative movement of ball 5 is dependent only on whether the change in nozzle backpressure results in a force change sufiicient to change the direction of the net force due to supply pressure or pressures acting on stem 6, and is independent of the particular scheme adopted for biasing diaphragm l4 upwards. If stem 6 were used to actuate an electrical contact-device, rather than a valve such as is defined by ball 5 and seats 7 and 8, it would be more convenient to use a spring for upward bias than the pressurized diaphragm 13.

The input force to the operator 0, namely, that which moves cup 39, could be other than a gas-operated bellows. For example, the same regenerative action could be obtained if the force exerted by bellows 38 were due to a head of liquid therein. On the other hand, what may be called a rigid input device, such as a liquid-filled temperature-responsive system having a bellows expanding and contrasting in correspondence to volumetric changes in the system-liquid would not cause the described regenerative action with direct coupling between said bellows, say, and said cup. However, if a compression spring were inserted between said bellows and said cup so that expansion of said bellows was translated into an elastic force acting on said cup in the fashion of the described bellows 38, then the characteristic regenerative action would be obtained. On the other hand, temperature responsive systems of the gas, or of the vapor pressure type, due to the inherent elasticity of gas and of vapor, would not require the extra spring.

In FIGURE 1 is also shown a refinement of the unloading scheme just described, namely, a pneumatic switch or valve S arranged to cause unloading on start-up of the compressor. Switch S includes a tubular casing 45 having slidably received therein a pair of seals 46 and 47, seal 47 being of sufiicient size to close off a port 48 in the side of casing 46, and the two seals being spaced sutficiently far apart on a stem 50, that if the stem 50 is pushed downward against the bias of a spring 51 pushing against an enlargement or collar 52 of stem 50, so as to uncover port 48, a port 49 in the side of casing 45 will communicate via the space between seals 46 and 47 with port 48. Now operation of operator as described supra depends on communication between passages 27 and 28. Left to itself, however, spring 51 maintains seal 46 in front of port 48 so that port 49 dead-ends between seals 46 and 47. As is obvious, if air is then supplied port 23, there will be no communication of nozzle 31 with passage 27, and, hence, pressure in chamber 19 will build-up to the point of tripping the operator and unloading the compressor. If now switch S is provided with an actuator such as an armature 53 and a solenoid 54, which when electrically energized is capable of driving the armature 53 down against the bias of spring 51. so as to move seals 46 and 47 far enough to bridge ports 48 and 49, so that nozzle 31 will bleed the pressure from chamber 19 and ball will be driven to seat 8 to load the compressor C, the operator 0 may be caused to automatically unload compressor C when it is first started up. All that is necessary is to provide a speed responsive switch G, or the like, e.g., a centrifugal electrical switch arranged to sense the speed of motor M and set to connect a source of electrical energy E across the ends of solenoid 54- when the motor M is up to speed. The operation is obvious but, in brief, solenoid 54 will be de-energized as long as Motor M is at a standstill or not up to speed, hence passage 27 will be blocked off from nozzle 31 and the valve V will be held open so that when compressor C is started up it is unloaded. However, as soon as motor M is up to speed, switch G will energize solenoid 54, seals 46 and 47 will be driven down so as to connect nozzle 31 and passage 27, and the operator 0 will load the compressor. If desired, a manual switch 55 can be utilized to break the solenoid circuit as an emergency measure for use in manual unloading while motor M is up to speed. Those skilled in the art will be aware of expedients other than a motor speed sensing device for automatically energizing solenoid 54 when the motor is up to speed.

FIGURE 2 shows that nozzle 31 has an axial bore 31a opening into a ball chamber 311:. Chamber 31b is somewhat larger than ball 32, but is so proportioned that if ball 31 is esated on the upper end of bore 31a, a part of the ball projects through an opening 31c in chamber 31b. Opening 310, however, is of lesser diameter than ball 31, yet large enough to allow the ball to move off the end of bore 31a. Hence, if one or more apertures such as 31d are provided in the side of chamber 31b, pressure fiuid admitted to bore 31a can blow ball 32 off the upper end of the bore 31a and escape through aperture 31d, even though ball 32 may seat in aperture 310. On the other hand, the bottom of cup 39 can contact the ball 32 and prevent the pressure fluid from lifting the ball from the top opening of bore 31b.

Naturally, other types of heme and nozzle devices can be used, but for the preferred construction of operator 0 shown in FIGURE 1, the ball-type bleed device is particularly suitable since it is both compact and rugged. Moreover, once the operator 0 is assembled, ball 32 is inherently and permanently properly aligned for throttling nozzle 31 under the control of cup 39.

Nozzle 31 could be screwed up or down in projection 43 for the purpose of adjusting the set point of the operator 0. However, it is more convenient to do this by adjusting spring 40. Thus, collar 42 would be screwed up in order to increase the value of receiver pressure needed to drive cup 39 down against ball 32.

If desired, spring 44 can be arranged to permit adjustment of its effective spring constant so as to permit adjustment of the width of the dead spot of the operator without changing springs. FIGURE 3 shows one of several generally known ways of adjusting the effective spring constant of a spring such as spring 44, that might be utilized in our novel operator 0. In this case, stem 6 terminates in a shortened portion 6a. Resting on the upper end of portion 6a is what amounts to a bolt having a threaded shank 58 and a head 59, the total length of the bolt being enough less than the distance between cup 39 and 6a that the upper end of shank 58 never is contacted by cup 39. A spring seat having a nut 60 threaded on shank 58 grips the spring 44 as by clasps 61 and 62 secured to nut 60. Hence, to adjust the number of free turns in spring 44, and therefore its effective spring constant, it is only necessary to remove the said bolt, thread the desired amount of spring through clasps 61 and 62, and then thread the nut 60 along shank 58 until the original length of the assembly from head 59 to the cupcontacting end of spring 44 is restored.

It will be appreciated that a plurality of operators 0 may be necessary in some unloading schemes. A threestep scheme, for example, is often used, since it allows wear on the two clearance pockets or other unloading devices needed in a three-step scheme to be equalized. That is, if the compressor use tends to center around the middle step of the scheme where only one pocket is used, it is only necessary to adjust the springs 40 of the two operators used in order to interchange in the unloading scheme the pocket and operator involved in the relatively little-used third step (full unload, say) and the pocket and operator involved in the more frequently used second step.

It is not necessary to illustrate a three-step scheme, since it is simply a matter of paralleling parts of FIG- URE 1, to wit a second operator having its input connected to receiver R, a second valve V connected to the output of the second operator, a second pocket P, and, if automatic unloading on start up is necessary or desired, a second pneumatic switch S, or equivalent, connected to 9 the second operator to be actuated along with the illustrated switch S so that both pockets are effective until motor M comes up to speed.

However, FIGURE 4 has been added to show briefly a dual operator which in eflect is simply two operators 0 such as shown in FIGURE 1. It is convenient to provide the dual operator with a common body part 100 instead of two separate body parts 1. Likewise, the two operators may share a common supply connection (not shown), a common body part 400, and a common receiver pressure connection 360, corresponding to connection 23, body part 4 and connection 36, respectively, in FIGURE 1. The remainder of each operator 0 in FIGURE 4 is identical to what is shown in FIGURE 1, as indicated by use therein of reference numerals 2, 3, 12, 25 and 40 having the same significance as in FIGURE 1.

Obviously, our novel operator 0 is not restricted in its utility to compressor unloading, although it is ideally suited thereto by reason of its snap-acting ball 5 and its dead spot characteristic. Moreover, it will be noted that the particular structural form shown in FIGURE 1 is unusually compact and rugged, due to the fact that the bleed device utilized, i.e., ball 32 and nozzle 31, is located within the confines of spring 40. Hence, the operator O everywhere presents to the exterior a solid, sturdy structure entirely void of wasted volume or delicate elements exposed to damage from the exterior.

Accordingly, it is not to be thought that our invention is restricted to any particular art, application or form other than according to the terms of the various claims appended hereto.

In accordance with the patent statutes we have pro vided a full, clear, concise and exact description of our invention including the best mode of carrying it out now known to us. However, it is to be understood that those skilled in the art will be aware of many obvious changes and applications of our invention falling within the scope of the following claims.

We claim:

1. In a regenerative relay, condition responsive means movable in response to a condition, spring means biasing said condition responsive means, said condition responsive means and said spring means being so constructed and arranged that the extent of motion of the former is a function of the spring constant of said spring means and the magnitude of said condition; movable means movable in response to a predetermined extent of movement of said condition responsive means, and constructed and arranged to relieve by its movement some of the bias efiect of spring means on said condition responsive means whereby said condition responsive means executes further movement by reason of the decrease in net bias resulting from movement as aforesaid of said movable means.

2. The invention of claim 1 wherein said spring means includes first and second spring devices, said first spring device being arranged to exert a bias on said condition responsive means, said bias being a function of the distance between said condition responsive device and a fixed point relative to which both said condition responsive means and said movable means move, said second spring device being arranged to exert a bias on said condition responsive device that is a function of the distance between said movable means and said condition responsive means.

3. In combination, a first wall movable in response to pressure applied thereto, a second wall movable in response to pressure applied thereto, first bias means for elastically opposing movement of said first wall substantially in proportion to the magnitude of pressure applied thereto, second bias means for preventing movement of said second wall until the pressure applied thereto attains a given magnitude, control means operable by said first wall to increase the pressure applied to said second wall, said first wall and said second wall being arranged so that movement of said first wall to a predetermined extent in response to increase in pressure applied thereto causes said control means to increase pressure applied to said second wall so as' to move said second wall; said first bias means being responsive to movement of said second wall against the bias of said second bias means to reduce the opposition of said first bias means to movement of said first wall, whereby if the pressure applied to said first wall is such as to cause said control means to increase pressure applied to said second wall enough to cause said second wall to move against the bias of said second bias means, the reduction of the opposition of said first bias means to movement of said first wall will result in further movement of said first wall such as to cause said control means to fiur-ther increase the pressure applied to said second wall, and so on, the net result being that movement of said second wall occurs regeneratively.

4. In combination, a hollow body having an abutment, an expansible chamber having a portion movable in response to pressure toward said abutment, and spring means between said abutment and said portion, said spring means being arranged to be stressed upon motion of said portion toward said abutment; a diaphragm in said body forming the movable wall of a chamber in said body and responsive to pressure in said chamber to move away from said portion, means for supplying fluid pressure to said chamber, a nozzle connected to said chamber for preventing fluid pressure from building up in said chamber unless said nozzle is baffled, a baffie spaced from said nozzle, said bafile being arranged to produce a baflling effect on said nozzle in response to a predetermined extent of movement of said portion toward said abutment, whereby if fluid pressure is supplied to said chamber said predetermined extent of movement results in build-up of pressure in said chamber, further spring means connected between said diaphragm and said portion and arranged to elastically transmit motion of said portion toward said abutment to said diaphragm so as to tend to move said diaphragm away from said portion, and stress said further spring means. unless said diaphragm moves away from said portion, whereby if said predetermined extent of movement occurs and pressure builds up enough in said chamber to move said diaphragm away from said portion, said stress will relax so as to permit further movement or" said portion toward said abutment and thus increase baffling of said nozzle.

5. The invention of claim 4 including a further diaphragm in said body forming a movable wall of a further chamber in said body, said further diaphragm being arranged to move toward said portion in response to pressure in said further chamber, means connecting said diaphragms, and means for supplying pressure to said further chamber for biasing both said diaphragms against movement away from said portion unless fluid pressure builds up in the first-mentioned chamber to an extent suflicient to overcome the eflfect of pressure in said further chamber.

6. A fluid pressure relay comprising, in combination, a cup having radially outwardly projecting flange means at the mouth thereof, a bellows means in said cup having a free end adjacent the bottom of said cup and a fixed end adjacent the mouth of said cup; a support to which said fixed end is secured; an abutment spaced from and generally facing the external surface of said bottom, spring means extending between said flange means and said abutment, said spring means being arranged to resist motion of said cup toward said abutment; motion detecting means between said abutment and said bottom, said motion detecting means being arranged to detect motion of said bottom relative to said abutment, means for applying fluid pressure within said bellows means; said relay also including a wall movable in response to fluid pressure applied to the surface thereof; said wall being mounted to move thusly along the line of movement of said bottom, being positioned so that said abutment lies between said bottom and said wall, and being provided with a bias tending to cause movement of said wall toward said bottom; means for applying fluid pressure to said wall so as to move said wall away from said bottom against said bias, and said motion detecting means being responsive to a predetermined extent of movement of said bottom toward said abutment to cause said means for applying fluid pressure to apply fluid pressure to said wall; resilient means for elastically transmitting said bias to said bottom so as to oppose movement of said bottom toward said abutment; whereby if the pressure within said bellows means suffices to move said bottom said predetermined extent against the resistance of said spring means and said elastic means, fluid pressure will be applied to said well so as to decrease the effect of said bias on said bellows means and assist movement of said bottom toward said abutment.

7. In combination, a nozzle, and bafiie means for said nozzle; first pressure responsive means for receiving a pressure, said first pressure responsive means being movable in a given direction to cause said baffle means to throttle said nozzle when said pressure changes in a given sense to a given magnitude, said first pressure responsive means being movable in a direction opposite to said given direction if said pressure changes in a sense opposite to said given sense; elastic bias means arranged to oppose movement of said first pressure responsive means; pressure fluid supplying means for said nozzle;

second pressure responsive means arranged to be responsive to pressure in said nozzle and to decrease the opposing effect of said elastic bias means relative to movement of said first pressure responsive means, in said given direction; whereby upon throttling of said nozzle by said bafile means, a regenerative increase of the pressure in said nozzle occurs and causes movement of said second pressure responsive means, and if said nozzle becomes unbaflied by said bafiie means, a regenerative decrease in the pressure in said nozzle occurs; and openable and closable valve in said nozzle, said valve when closed being arranged to give the effect of baffling said nozzle; and control effect producing means responsive to movement of said second pressure responsive means to produce a control efiect having a sense corresponding to the sense of movement of said second pressure responsive means.

References Cited in the file of this patent UNITED STATES PATENTS 2,274,337 Ritter Feb. 24, 1942 2,301,034 Freeman et a1. Nov. 3, 1942 2,724,555 Roetter Nov. 22, 1955 2,780,230 Freeman *Feb. 5, 1957 2,781,770 Sutton Feb. 19, 1957 

